Pedicle Screw Insertion System and Method

ABSTRACT

Improved methods and apparatuses for inserting pedicle screws in accordance with embodiments of the present invention include an image correction algorithm. In various embodiments, an original image of a region of interest of a patient including a pedicle is created with an X-ray emitter and an X-ray detector. Due to the X-ray emitter not being aligned orthogonal to the X-ray detector, the original image will be skewed. Using a known location and orientation of the X-ray detector, a location and orientation of the X-ray emitter provided by a position monitoring system, and the original image, a processing system can execute the image correction algorithm to provide a corrected image to allow a surgeon to properly insert a pedicle screw along the axis of the pedicle while viewing an accurate corrected image in real time.

RELATED APPLICATION

This application is a continuation of Application Ser. No. 13/094,527filed Apr. 26, 2011, which claims the benefit of U.S. ProvisionalApplication No. 61/328,062 filed Apr. 26, 2010, each of which is herebyfully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to apparatuses and methods for insertingpedicle screws. More specifically, the present invention relates to apedicle screw drill system and method that utilizes x-ray imaging toplace pedicle screws along the axis of the pedicles when the x-raysource is not orthogonal to the base.

BACKGROUND OF THE INVENTION

Pedicle screw fixation is an increasingly important technique in spinesurgery. Pedicle screws are inserted into the vertebrae or spinal columnof a patient in order to make it possible for a spinal column of apatient suffering from a traumatic or degenerative disease to performits proper function. Accurate placement of pedicle screws is vital toavoid iatrogenic injuries to nervous or vascular structures. Accurateplacement of the screws in the vertebral body also yields greater bonypurchase, therefore increasing pull out strength. Currently, there are anumber of methods used to insert pedicle screws into the spine of apatient.

One method of inserting pedicle screws involves blind placement of thescrews by a physician. The physician, guided only by sight, drills theholes based on the physician's experience and knowledge of the spine.Such a technique can be effectively practiced only by highly skilled andexperienced practitioners and is generally considered a whollyinadequate and not recommended procedure.

Intra-operative navigations systems such as, for example, the MedtronicStealthStation® and Stryker® Navigation Systems, are also used forplacement of pedicle screws. These systems provide markers and otherstructures to guide the physician's drilling process. However, suchsystems are expensive, add significant time to the surgical proceduredue to setup, and can suffer from intra-operative shifting of structuresand registration error.

Another technique for placement of pedicle screws utilizes traditionalfluoroscopic x-ray techniques. This involves the use of standard x-raysystems, such as C-arms, to image the target pedicle area as thephysician drills. Such systems are economical and provide real time datawhich eliminates intra-operative shift of structures and registrationerrors. However, they are typically limited to use withanterior-posterior and lateral projections. These systems are alsosuboptimal when the pedicle sits at angles that are not orthogonal tothe base of the X-ray system. In addition, C-arm x-ray systems are largeand cumbersome, so repositioning for a procedure can be a lengthyprocess.

It would be desirable to provide an X-ray directed pedicle screw drillsystem designed to replace existing methods for drilling pedicle screwswith a faster and more accurate system that exposes the patient to aminimal amount of X-ray radiation

SUMMARY OF THE INVENTION

Improved methods and apparatuses for inserting pedicle screws inaccordance with embodiments of the present invention include an imagecorrection algorithm. In various embodiments, an original image of aregion of interest of a patient including a pedicle is created with anX-ray emitter and an X-ray detector. Due to the X-ray emitter not beingaligned orthogonal to the X-ray detector, the original image will beskewed. Using a known location and orientation of the X-ray detector, alocation and orientation of the X-ray emitter provided by a positionmonitoring system, and the original image, a processing system canexecute the image correction algorithm to provide a corrected image toallow a surgeon to properly insert a pedicle screw along the axis of thepedicle while viewing an accurate corrected image in real time.

In one embodiment, a system for inserting a pedicle screw into a pedicleof a patient utilizes an image correction algorithm. System can includea manually positionable X-ray emitter including a drill assembly forinserting the pedicle screws. An X-ray detector can detect the X-raysfrom the X-ray emitter and generate an original image of a region ofinterest between the X-ray emitter and X-ray detector including thepedicle. A position monitoring system can monitor a position andorientation of the X-ray emitter. A processor operably connected to theposition monitoring system and the X-ray detector can execute an imagecorrection algorithm operable to provide a corrected image from theoriginal image due to the original image being skewed as a result of theX-ray emitter not being perpendicular to the X-ray detector. A videodisplay can display the corrected image in real-time to a surgeonperforming an operation to insert the pedicle screw into the pedicle ofthe patient.

In another embodiment, a method includes providing a system forinserting a pedicle screw into a pedicle of a patient. The system caninclude a manually positionable X-ray emitter including a drillassembly, an X-ray detector that detects the X-rays from the X-rayemitter, a position monitoring system that monitors a position andorientation of the X-ray emitter, a processor that executes an imagecorrection algorithm and a video display. The method can further includeinstructions for inserting the pedicle screw into the pedicle of thepatient. The instructions can include manually positioning the X-rayemitter in more than three degrees of freedom at an insertion angle thatis axially aligned with the pedicle and that is not perpendicular to theX-ray detector to obtain an original image of a region of interestincluding the pedicle, which results in the original image being skewed.The instructions further comprise viewing a corrected image of theregion of interest on the video display that result from application ofthe image-correction algorithm to the skewed original image andinserting the pedicle screw with the drill assembly while viewing thecorrected image in real-time.

The above summary of the various embodiments of the invention is notintended to describe each illustrated embodiment or every implementationof the invention. This summary represents a simplified overview ofcertain aspects of the invention to facilitate a basic understanding ofthe invention and is not intended to identify key or critical elementsof the invention or delineate the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 depicts a pedicle screw insertion system according to anembodiment of the present invention.

FIG. 2 depicts a pedicle screw insertion system according to anembodiment of the present invention.

FIG. 3A depicts an X-ray emitter gun according to an embodiment of thepresent invention.

FIG. 3B is a cross-sectional view of the X-ray emitter gun of FIG. 3A,taken at the midplane of the gun looking into the page.

FIG. 4 depicts a flowchart of steps of an image correction algorithmaccording to an embodiment of the present invention.

FIG. 5A is a view of an object and original and corrected Images of theobject according to an embodiment of the present invention.

FIG. 5B is another view of an object and original and corrected imagesof the object according to an embodiment of the present invention.

FIG. 6 depicts the use of a pedicle screw insertion system according toan embodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the presentinvention. However, one skilled in the art will recognize that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as to not unnecessarily obscure aspects ofvarious embodiments of the present invention.

Referring to FIG. 1, a schematic representation of a pedicle screwinsertion system 100 according to an embodiment of the present inventionis depicted. System 100 generally includes an X-ray emitter 104 and anX-ray detector 102 for detecting the X-rays generated by emitter 104.X-ray emitter 104, as described more fully herein, can also incorporatea drill for inserting pedicle screws into the spine of a patient. System100 can also include a position monitoring system 106 to track or sensethe movements of the emitter 104 in any number of degrees of freedom. Aprocessor executing a computer-implemented image correction algorithm108 can be used, as described more fully herein, to provide a moreaccurate image of the X-rayed region to a surgeon, who views thecorrected image on a monitor or display 110 in real-time.

The X-ray detector 102 is placed beneath/opposite the patient in thearea of interest, i.e., the area where pedicle screws are going to beplaced. In one embodiment, X-ray detector 102 is a planar flat-paneldetector mounted beneath the patient table and on an X/Y movable stageallowing it to be positioned under the area of interest of the patientas needed. Such modem flat-panel detectors are advantageous in that theyare light weight, can run high frame-rates, use fewer parts and canprovide an immediate digital image. Various flat-panel X-ray detectorsthat can be used with embodiments of the present invention aremanufactured by Varian Medical Systems of Palo Alto, Calif.

In one embodiment, detector 102 provides at least near real-timefeedback to the surgeon. In this embodiment, detector 102 can acquireimages at a frame rate of at least 15 frames per second. It has beenobserved that at rates of higher than 25 frames per second it isdifficult to discern meaningful differences in detected images as aresult of such higher rates, so a range of frame rates of 15 frames persecond to 25 frames per second is preferred. Ideally, the system 100uses the largest flat-panel detector 102 that can provide such aresponse time in the desired range of frame rates. In one embodiment,such response times can be provided by a 16″ by 12″ detector 102.

The X-ray emitter 104 can be a handheld X-ray gun that can include anX-ray source, such as an X-ray tube having an anode, a cathode, and apower source, located behind an actuator for inserting pedicles screwsinto a spine of a patient, such as a drill bit and drive assembly. Inone embodiment, the drill bit and drive mechanism, such as a planetarygear system, are X-ray translucent so as not to interfere with theemitted X-rays. In this embodiment, at least the portion of the drillassembly that is coaxial with an axis of insertion of the pedicle screwis X-ray translucent. This provides an unobstructed image as the screwis inserted, which allows the surgeon to image the target at the sametime as drilling for the screw without the need for a separate X-raydevice. One embodiment of an X-ray translucent drill mechanism, aspectsof which can be used in embodiments of the present invention, isdisclosed in U.S. Pat. No. 5,013,317 to Cole et al., which isincorporated herein by reference. In another embodiment, drill assemblycan be aligned to operate on an axis that is parallel to, but does notoverlap with, the axis along which the X-rays are emitted, so as not tobe positioned between the X-ray emitter and detector while still beingaligned at the same angle.

An X-ray emitter 104 in the form of a handheld X-ray drill gun accordingto an embodiment of the present invention is depicted in FIGS. 3A and3B. X-ray gun 104 is lightweight and easily maneuverable by a surgeonand includes a handle 115 connected to a housing 116. Housing contains adrill mechanism 118, which as noted above can by X-ray translucent, andan X-ray source 122. In one embodiment, the X-ray source is positionedbehind the drill mechanism 118 in the housing. Drill mechanism 118 canbe provided with variously sized interchangeable drill bits 120 that canform pilot holes in the pedicles. Drill mechanism 118 can insert thepedicle screws into the pilot holes or can directly insert pediclescrews without first forming pilot holes. In some embodiments, X-ray gun104 can be about the size of a modem cordless drill, allowing thesurgeon to move about freely with the device in order to locate the axisof the pedicle. In one embodiment, X-ray emitter can be provided with asafety feature that only allows X-rays to be emitted when it is aimed atthe detector, to prevent unnecessary and potentially harmful emission ofX-rays.

A position monitoring system 106 is used in system 100 because propervisualization of the procedure requires knowing where the X-ray emitter104 is positioned and oriented in space. In some embodiments, thedetector 102 does not need to be tracked by the position monitoringsystem 106 because it maintains a fixed orientation in space afterinitially being set for the procedure, so its location and orientationare known. In other embodiments, the surgeon can adjust the detector 102during the procedure so its location and orientation can also betracked.

Position monitoring system 106 must be compatible with a nearby X-raysource, tolerant of significant metal in the environment, and have highreliability and accuracy. In some embodiments, position monitoringsystem 106 can be an optical tracking system, such as manufactured byAscension Technology Corporation of Milton, Vt. In other embodiments,positioning monitoring system 106 can be a kinematic/mechanical trackingvia an arm or linkage. In such an embodiment, the X-ray emitter/gun canbe attached to a manually positionable arm anchored to a ceiling, wallor floor of an operating room or a movable base in 20 the operatingroom. In other embodiments, position monitoring system can useradio-frequency identification, image analysis using infrared light, orother wireless tracking/sensing. In some embodiments, some or all ofposition monitoring system 106 can be incorporated into X-ray emitter104 rather than being a separate system. In such embodiments, positionmonitoring system 106 can use one or more of accelerometers,gravitometers, magnetometers, and global positioning systems to trackand/or sense the location and orientation of emitter 104. Positionmonitoring system 106 can allow the emitter to be positionable, andtrack the positioning of the emitter, in at least three or more degreesof freedom. In some embodiments, the emitter can be positionable in fiveor six degrees of freedom. In one embodiment, emitter can be lockable toprevent movement in one or more degrees of freedom for all or part ofthe procedure, such as only allowing the emitter to be moved along theaxis of insertion once proper alignment has been obtained.

Tracking the X-ray emitter's 104 location and orientation relative tothe detector 102 and imaged area allows the use of a perspective imagecorrection algorithm to eliminate the need to keep the gun perpendicularto the plate, giving the surgeon a great deal of freedom of movement ininserting pedicle screws. This is desirable because the pedicle is oftennot aligned perpendicular to the detector and each pedicle may have adifferent alignment. To properly place pedicle screws, the pilot holemust be accurately drilled axially down the pedicle. However, aligningthe emitter/drill 104 axially with the pedicle causes it to be at angleto the detector 102, which results in a skewed image being detected andgenerated by the detector. Use of an image correction algorithm allowsthe surgeon to align the X-ray gun at an angle to the detector that isperpendicular to the pedicle (regardless of the alignment of the pediclerelative to the detector) for inserting the pedicle screw whilevisualizing an accurate image of the pedicle.

The image correction algorithm 108 therefore allows the X-ray emitter104 to be used in alignments that are not orthogonal to the X-raydetector 102 when the emitter 104 is being used to image the area ofinterest 112 of the patient on the patient table 114, as depicted inFIG. 2. The skewed image resulting from non-orthogonal alignment of theemitter 104 and detector 102 can typically result in misaligned pilotholes (i.e., not axially aligned) for the pedicle screws. The imagecorrection algorithm 108 corrects this skewed image so that a true imageis shown to the surgeon in real time, allowing for more accurateplacement of pedicle screws. It should also be noted, as can be seen inFIG. 2, that the thickness of the table 114 combined with the thicknessof the patient 112 places a geometric limit on the angle at which theX-ray emitter 104 can be used relative to the area of interest 112 inorder to be captured by the detector 102.

In one embodiment as shown in FIG. 4, the image correction algorithm108, which can be executed by a processor, operates directly on thetexture coordinates of the original image recorded by the detector 102using matrix transforms. Transform matrices are a consistent way ofrepresenting linear transforms in a computational format. Byrepresenting object locations as vectors, e.g., f=(x, y, z), thoseobjects may be transformed in space (to f) by multiplying them with atransform matrix T such that f=Tf. If the detector 108 dimensions andit's transform in space D are known, the location of the four corners ofthe detector 102 can be defined with these methods at step 140 in asingle 4×4 matrix C, where x1, y1 and z1 (obtained from D and detector102 geometry) are a first corner of the detector 102 and so on up to x4,y4 and z4. The fourth element of each corner's vector represents thescale of each vector, which may be set to 1.

$C = \begin{bmatrix}{x\; 1} & {x\; 2} & {x\; 3} & {x\; 4} \\{y\; 1} & {y\; 2} & {y\; 3} & {y\; 4} \\{z\; 1} & {z\; 2} & {z\; 3} & {z\; 4} \\1 & 1 & 1 & 1\end{bmatrix}$

Standard texture coordinates ranging from 0 to 1 can then be assigned tothe four corner points at step 142. Texture coordinates (or UVcoordinates) are a tool used to linearly map a two-dimensional imageonto a three-dimensional object in space. These coordinates, usuallyrepresented as u and v, are assigned across an image, ranging from 0 to1 in each direction. Each vertex of the three-dimensional object isassigned a u and v coordinate indicating which part of thetwo-dimensional image is associated with that vertex. Since the detectorplate is rectangular and is covered by the detected image, the fourcorners (or vertices) of the detector map correspond to the four cornersof the detected image. These four texture coordinates are packed into atexture matrix T.

$T = \begin{bmatrix}0 & 1 & 1 & 0 \\0 & 0 & 1 & 1\end{bmatrix}$

By treating the X-ray emitter 104 as something of an imaginary camera, aperspective transformation for the field of view (“fov”) onto thedetector 102 can be defined using a standard perspective transformmatrix at step 144. Preferably, the fov is computed to be just largeenough to view the whole detector plate from the emitter's location. Inmost applications, a field of view of 45 degrees is sufficient. Aperspective transform matrix alters the shape of a given geometry tomatch the view of that geometry from a defined location. It addsperspective to the resulting image, such as by causing portions of thegeometry that are further away to be smaller. This mimics the view aswould be seen by the human eye from the defined location.

$P = \begin{bmatrix}\frac{1}{h} & 0 & 0 & 0 \\0 & \frac{1}{h} & 0 & 0 \\0 & 0 & \frac{\left( {{far} + {near}} \right)}{\left( {{near} - {far}} \right)} & \frac{\left( {2\mspace{14mu} {far}\mspace{14mu} {near}} \right)}{\left( {{near} - {far}} \right)} \\0 & 0 & {- 1} & 0\end{bmatrix}$

Where h=tan(fov/2) and far and near are the distances to the far andnear view planes. For optimal viewing, near is set at 1 and far is thedistance between the X-ray emitter 104 and the furthest corner of thedetector 102. Next, the gun/emitter transform matrix G (obtained fromthe position monitoring system) can be used to bring the detector 102corners into the image of the imaginary camera, C*, at step 146.

Finally, the corrected image is obtained at step 148 by rasterizing theimage space corners C* as a quadrilateral textured with the originaldetector image, by interpolating according to the texture coordinates.Rasterization is a standard computer graphics algorithm, which is knownto those skilled in the art. Rasterization, also known as scanconversion, is the process of rendering a three-dimensional shape orscene onto a flat two-dimensional surface, usually so it can be viewedon a monitor. Rasterization is used as part of the image correctionalgorithm 108 to render the transformed detector plate object (texturedwith its detected image) into the view space of the imaginary cameralocated at the gun/emitter. This yields the corrected image. In oneembodiment, the image correction algorithm is performed by a desktop orlaptop computer. In other embodiments, the algorithm can be performed bya processor within the emitter 104 or detector 102 or associated withthe monitor or display 110. In one embodiment, the algorithmcontinuously runs during the operation to provide a continuous real-timecorrected image that adjusts for movements of the emitter 104, detector102 or region of interest.

Corrected/Mage=Rasterize (C*, T, OriginalImage)

By defining the field of view and near/far planes as described herein, aminimum of information is lost during the image correction process. Noscaling is required to obtain a properly sized corrected image. Theentire process can also be implemented using modem graphics hardware.Corrected images can therefore be processed at extremely high framerates on the order of hundreds of times per second even for largeimages.

FIGS. 5A and 5B depict results of such image corrections. In FIG. 5A, acylindrical object 130 is being viewed with the X-ray emitter 104 alongthe vertical axis of the object. On the left the original image 132result as initially detected by the X-ray detector 102 is displayed.Because of the angle between the emitter 104 and the detector 102, theimage 132 is skewed. The corrected image 134 as displayed on a monitor110 following application of the image correction algorithm 108described herein to the image 132 recorded at the detector, which as canbe seen is identical to the actual image 130, is displayed on the right.FIG. 5B depicts a view of a cylindrical object 130 from an oblique anglewith the X-ray emitter 104. Similarly, the original image 136 asdetected by the X-ray detector 102 is skewed, whereas the correctedimage 138 displays the actual appearance of the object 130 from theoblique angle.

Referring now to FIG. 6, there can seen the result of such an imagecorrection during a procedure being performed on a patient 113 on apatient table 114 according to an embodiment of the present invention.The view in the Figure is taken down the emitting axis of an X-rayemitter at an angle to the detector. The original skewed image 152generated by the detector is corrected with the processor operating theimage-correction algorithm and is displayed as a corrected image 154that shows the actual appearance 150 of the patient's spine/pedicle fromthe angle on the monitor 110.

The monitor or display 110 need only be safe for use in an operatingroom and large enough to be easily observed by a surgeon whileperforming an operation. The monitor must be sterile if located withinthe sterile field of the procedure. If the monitor is not within thesterile field, it will not have to be sterile but will have to be largerthan a monitor within the sterile field in order to be viewable fromwithin the sterile field. In one embodiment, the display can be part ofthe X-ray emitter gun, such as a video screen located on a proximal endof the gun.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the present invention. It should beappreciated, moreover, that the various features of the embodiments thathave been described may be combined in various ways to produce numerousadditional embodiments. Moreover, while various materials, dimensions,shapes, implantation locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

1-23. (canceled)
 24. A system for inserting a pedicle screw into apedicle of a patient, comprising: a manually positionable beam emitteradjustable in more than three degrees of freedom, the emitter includinga drill assembly adapted to insert a pedicle screw into a pedicle of apatient along an axis of operation; a detector that detects a beam fromthe emitter, the beam oriented along an axis parallel to the axis ofoperation of the actuator, and generates an original two-dimensionalsurface projection image of a three-dimensional object having a regionof interest between the detector and emitter; a computer controlledposition monitoring system that monitors a position and an orientationof the emitter in the more than three degrees of freedom; a processoroperably connected to the position monitoring system and the detectorand configured to execute an image correction algorithm, the imagecorrection algorithm operable to provide a corrected two-dimensionalsurface projection image from the original two-dimensional surfaceprojection image, the original two-dimensional surface projection imageof the pedicle being skewed when the axis along which the beam isemitted is at an angle that is not perpendicular to the detectorrelative to an actual appearance of the pedicle and the correctedtwo-dimensional surface projection showing the actual appearance of thepedicle; and a video display linked to the processor to display thecorrected two-dimensional surface projection image in real-time to asurgeon performing an operation to insert the pedicle screw into thepedicle of the patient.
 25. The system of claim 25, wherein the imagecorrection algorithm executed by the processor operates directly ontexture coordinates of the original two-dimensional surface projectionimage generated by the detector using matrix transforms.
 26. The systemof claim 25, wherein the image correction algorithm executed by theprocessor utilizes rasterization to provide the correctedtwo-dimensional surface projection image.
 27. The system of claim 25,wherein the computer controlled position monitoring system is akinematic or mechanical tracking system.
 28. The system of claim 27,wherein the emitter is connected to an arm of the kinematic ormechanical tracking system.
 29. The system of claim 25, wherein thecomputer controlled position monitoring system is an optical trackingsystem.
 30. The system of claim 25, wherein the computer controlledposition monitoring system is at least partially located within theemitter.
 31. The system of claim 25, wherein the emitter is manuallypositionable in at least five degrees of freedom.
 32. The system ofclaim 25, wherein the axis of operation of the drill assembly and theaxis along which the beam is emitted are coaxial.
 33. The system ofclaim 32, wherein at least a portion of the drill assembly that iscoaxial with the axis along which the beam is emitted is comprised of amaterial that is translucent to the beam.
 34. The system of claim 25,wherein the emitter is an X-ray emitter and the detector is an X-raydetector.
 35. The system of claim 25, wherein the emitter is a handheldtool having a handle and a housing at least partially containing theactuator.
 36. A system for inserting a pedicle screw into a pedicle of apatient, comprising: a manually positionable X-ray emitter including adrill assembly adapted to insert a pedicle screw into a pedicle of apatient along an axis of operation; an X-ray detector that detects theX-rays from the X-ray emitter, the X-ray emitter capable of beingpositioned such that the X-rays are not perpendicular to the X-raydetector, wherein the X-ray detector generates an original image of aregion of interest that includes the pedicle when the pedicle ispositioned between the X-ray detector and the X-ray emitter; a computercontrolled position monitoring system that uses a processor to monitor aposition and an orientation of the X-ray emitter, wherein the processoris operably connected to the position monitoring system and the X-raydetector and configured to execute an image correction algorithm thatprovides a corrected image of the original image when the original imageis generated with the X-rays emitted at an angle that is notperpendicular to the X-ray detector; and a video display linked to theprocessor to display the corrected mage in real-time to a surgeonperforming an operation to insert the pedicle screw into the pedicle ofthe patient.